Chemical Reactions & Equations

What you'll learn

Understand what a chemical reaction is, how to balance equations using the law of conservation of mass, and the five main reaction types with everyday examples.

This chapter has

Chemical Reactions & Equations — solved practice questions

6 Class 10 Science questions with step-by-step solutions. Attempt each, then reveal the answer.

1. Q1easy

   Rusting of iron is an example of which type of reaction?

   • AReduction
   • BOxidation
   • CDisplacement
   • DDecomposition
   Show answer & solution

   Correct answer: (B) Oxidation

   Iron combines slowly with oxygen (and moisture) — it gains oxygen, so rusting is an oxidation reaction.

2. Q2easy

   In a balanced chemical equation, the number of atoms of each element is:

   • Amore on the left
   • Bmore on the right
   • Cequal on both sides
   • Dzero
   Show answer & solution

   Correct answer: (C) equal on both sides

   By the law of conservation of mass, atoms of each element must be equal on both sides of the equation.

3. Q3medium

   A reaction in which a single compound breaks down into two or more simpler substances is called:

   • ACombination
   • BDecomposition
   • CDisplacement
   • DDouble displacement
   Show answer & solution

   Correct answer: (B) Decomposition

   Breaking one compound into simpler ones is a decomposition reaction (e.g. 2H₂O → 2H₂ + O₂).

4. Q4medium

   When quicklime (CaO) reacts with water, the reaction is:

   • AEndothermic
   • BExothermic
   • CDisplacement
   • DReduction
   Show answer & solution

   Correct answer: (B) Exothermic

   CaO + H₂O → Ca(OH)₂ releases a large amount of heat, so it is an exothermic reaction.

5. Q5easy

   Which gas is released when zinc reacts with dilute hydrochloric acid?

   • AOxygen
   • BHydrogen
   • CCarbon dioxide
   • DNitrogen
   Show answer & solution

   Correct answer: (B) Hydrogen

   Zn + 2HCl → ZnCl₂ + H₂↑. Hydrogen gas is released.

6. Q6medium

   In a reaction, the substance that gains oxygen is said to be:

   • Areduced
   • Boxidised
   • Cneutralised
   • Devaporated
   Show answer & solution

   Correct answer: (B) oxidised

   Gaining oxygen (or losing hydrogen) is oxidation — so that substance is oxidised.

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